add example for java (#17850)

Author: harshil1712

src/content/docs/r2/examples/aws/aws-sdk-java.mdx

@@ -0,0 +1,204 @@
+---
+title: aws-sdk-java
+pcx_content_type: example
+---
+
+import { Render } from "~/components";
+
+<Render file="keys" />
+<br />
+
+This example uses version 2 of the [aws-sdk-java](https://github.com/aws/aws-sdk-java-v2/#using-the-sdk) package. You must pass in the R2 configuration credentials when instantiating your `S3` service client:
+
+```java
+import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
+import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
+import software.amazon.awssdk.regions.Region;
+import software.amazon.awssdk.services.s3.S3Client;
+import software.amazon.awssdk.services.s3.model.*;
+import software.amazon.awssdk.services.s3.S3Configuration;
+import java.net.URI;
+import java.util.List;
+
+/**
+ * Client for interacting with Cloudflare R2 Storage using AWS SDK S3 compatibility
+ */
+public class CloudflareR2Client {
+    private final S3Client s3Client;
+
+    /**
+     * Creates a new CloudflareR2Client with the provided configuration
+     */
+    public CloudflareR2Client(S3Config config) {
+        this.s3Client = buildS3Client(config);
+    }
+
+    /**
+     * Configuration class for R2 credentials and endpoint
+     */
+    public static class S3Config {
+        private final String accountId;
+        private final String accessKey;
+        private final String secretKey;
+        private final String endpoint;
+
+        public S3Config(String accountId, String accessKey, String secretKey) {
+            this.accountId = accountId;
+            this.accessKey = accessKey;
+            this.secretKey = secretKey;
+            this.endpoint = String.format("https://%s.r2.cloudflarestorage.com", accountId);
+        }
+
+        public String getAccessKey() { return accessKey; }
+        public String getSecretKey() { return secretKey; }
+        public String getEndpoint() { return endpoint; }
+    }
+
+    /**
+     * Builds and configures the S3 client with R2-specific settings
+     */
+    private static S3Client buildS3Client(S3Config config) {
+        AwsBasicCredentials credentials = AwsBasicCredentials.create(
+            config.getAccessKey(),
+            config.getSecretKey()
+        );
+
+        S3Configuration serviceConfiguration = S3Configuration.builder()
+            .pathStyleAccessEnabled(true)
+            .build();
+
+        return S3Client.builder()
+            .endpointOverride(URI.create(config.getEndpoint()))
+            .credentialsProvider(StaticCredentialsProvider.create(credentials))
+            .region(Region.of("auto"))
+            .serviceConfiguration(serviceConfiguration)
+            .build();
+    }
+
+    /**
+     * Lists all buckets in the R2 storage
+     */
+    public List<Bucket> listBuckets() {
+        try {
+            return s3Client.listBuckets().buckets();
+        } catch (S3Exception e) {
+            throw new RuntimeException("Failed to list buckets: " + e.getMessage(), e);
+        }
+    }
+
+    /**
+     * Lists all objects in the specified bucket
+     */
+    public List<S3Object> listObjects(String bucketName) {
+        try {
+            ListObjectsV2Request request = ListObjectsV2Request.builder()
+                .bucket(bucketName)
+                .build();
+
+            return s3Client.listObjectsV2(request).contents();
+        } catch (S3Exception e) {
+            throw new RuntimeException("Failed to list objects in bucket " + bucketName + ": " + e.getMessage(), e);
+        }
+    }
+
+    public static void main(String[] args) {
+        S3Config config = new S3Config(
+            "your_account_id",
+            "your_access_key",
+            "your_secret_key"
+        );
+
+        CloudflareR2Client r2Client = new CloudflareR2Client(config);
+
+        // List buckets
+        System.out.println("Available buckets:");
+        r2Client.listBuckets().forEach(bucket ->
+            System.out.println("* " + bucket.name())
+        );
+
+        // List objects in a specific bucket
+        String bucketName = "demos";
+        System.out.println("\nObjects in bucket '" + bucketName + "':");
+        r2Client.listObjects(bucketName).forEach(object ->
+            System.out.printf("* %s (size: %d bytes, modified: %s)%n",
+                object.key(),
+                object.size(),
+                object.lastModified())
+        );
+    }
+}
+```
+
+## Generate presigned URLs
+
+You can also generate presigned links that can be used to temporarily share public write access to a bucket.
+
+```java
+// import required packages for presigning
+// Rest of the packages are same as above
+import software.amazon.awssdk.services.s3.presigner.S3Presigner;
+import software.amazon.awssdk.services.s3.presigner.model.PutObjectPresignRequest;
+import software.amazon.awssdk.services.s3.presigner.model.PresignedPutObjectRequest;
+import java.time.Duration;
+
+public class CloudflareR2Client {
+  private final S3Client s3Client;
+  private final S3Presigner presigner;
+
+    /**
+     * Creates a new CloudflareR2Client with the provided configuration
+     */
+    public CloudflareR2Client(S3Config config) {
+        this.s3Client = buildS3Client(config);
+        this.presigner = buildS3Presigner(config);
+    }
+
+    /**
+     * Builds and configures the S3 presigner with R2-specific settings
+     */
+    private static S3Presigner buildS3Presigner(S3Config config) {
+        AwsBasicCredentials credentials = AwsBasicCredentials.create(
+            config.getAccessKey(),
+            config.getSecretKey()
+        );
+
+        return S3Presigner.builder()
+            .endpointOverride(URI.create(config.getEndpoint()))
+            .credentialsProvider(StaticCredentialsProvider.create(credentials))
+            .region(Region.of("auto"))
+            .serviceConfiguration(S3Configuration.builder()
+                .pathStyleAccessEnabled(true)
+                .build())
+            .build();
+    }
+
+    public String generatePresignedUploadUrl(String bucketName, String objectKey, Duration expiration) {
+        PutObjectPresignRequest presignRequest = PutObjectPresignRequest.builder()
+            .signatureDuration(expiration)
+            .putObjectRequest(builder -> builder
+                .bucket(bucketName)
+                .key(objectKey)
+                .build())
+            .build();
+
+        PresignedPutObjectRequest presignedRequest = presigner.presignPutObject(presignRequest);
+        return presignedRequest.url().toString();
+    }
+
+    // Rest of the methods remains the same
+
+    public static void main(String[] args) {
+      // config the client as before
+
+      // Generate a pre-signed upload URL valid for 15 minutes
+        String uploadUrl = r2Client.generatePresignedUploadUrl(
+            "demos",
+            "README.md",
+            Duration.ofMinutes(15)
+        );
+        System.out.println("Pre-signed Upload URL (valid for 15 minutes):");
+        System.out.println(uploadUrl);
+    }
+
+}
+```